XPath with hiearchical matching - xpath

Question

** Edited for clarification **
I've inherited a bunch of xml documents (configuration files) that resemble the following structure (element names changes and structured simplified for the sake of brevity.
<containers>
<container id="c1">
<ports>
<port id="p2"/>
</ports>
<rules>
<!--
Within a container, a rule must refer to a port
declared within the same container.
A rule cannot refer to a port that does not
exist in the enclosing container.
-->
<rule id="r1" portId="p1"/><!-- p1 is not in c1, but in c2, bad -->
<rule id="r2" portId="p2"/><!-- this is good -->
<rule id="r3" portId="p3"/><!-- p3 is nowhere, bad -->
</rules>
</container>
<container id="c2">
<ports>
<port id="p1"/>
<port id="p2"/>
</ports>
<rules>
<rule id="r1" portId="p1"/>
</rules>
</container>
</containers>
A container can have points and rules (point and rule ids can be duplicated among containers; they just need to be unique within a container.)
The requirement is that if a rule references a point id, that point id must be defined within the enclosing container.
I need to search for rules within containers that, by mistake reference non-existing points.
I have xpath expressions that can find a rule that points to a non-existing point (unfortunately for the entire xml document.)
//*/rule/#portId[not( . = //*/port/#id)]
The rule applies to the entire document, it is not contained within containers.
That is, this xpath expression would detect that the rule r3 in container c1 refers to a port p3 that does not exist anywhere in the document.
However, this same xpath expression would not detect that rule r1 in container c1 refers to a port p2 that is not in container c1. Why? Because this xpath expression will match it with port p2 in container c2.
My xpath expression would not detect this.
Granted, I could do this with several xpath expressions and glue code between them (say, by applying the xpath expression to each container) but I was hoping if it is possible to use one single xpath expression starting from the root element instead.
Any advice?

Answer 1

Another option using the ancestor:: axis...
//rule[not(#portId = ancestor::container//port/#id)]

Answer 2

Try this one.
//rule[#portId[not(. = ./parent::rule/parent::rules/parent::container/*/port/#id)]]
This seems to work for me. Tested on:
<containers>
<container id="c1">
<ports>
<port id="p2"/>
<port id="p4"/>
</ports>
<rules>
<!--
Within a container, a rule must refer to a port
declared within the same container.
A rule cannot refer to a port that does not
exist in the enclosing container.
-->
<rule id="r1" portId="p1"/><!-- p1 is not in c1, but in c2, bad -->
<rule id="r2" portId="p2"/><!-- this is good -->
<rule id="r3" portId="p3"/><!-- p3 is nowhere, bad -->
</rules>
</container>
<container id="c2">
<ports>
<port id="p1"/>
<port id="p2"/>
</ports>
<rules>
<rule id="r1" portId="p1"/>
<rule id="r2" portId="p4"/>
</rules>
</container>
</containers>
using this online processor.
Got the following output
Element='<rule id="r1" portId="p1"/>'
Element='<rule id="r3" portId="p3"/>'
Element='<rule id="r2" portId="p4"/>'